QuestionIonic equilibrium / buffer
What will be the hydrogen ion concentration of a solution obtained by mixing 500 ml of 0.20 M acetic acid and 500 ml of 0.30 M sodium acetate? (Dissociation constant of acetic acid = 1.75 × 10⁻⁵)
- (a) 2.75 × 10⁻⁵ mol.dm⁻³
- (b) 1.17 × 10⁻⁵ mol.dm⁻³
- (c) 3.50 × 10⁻⁵ mol.dm⁻³
- (d) 1.75 × 10⁻³ mol.dm⁻³
Answer: (b) 1.17 × 10⁻⁵ mol.dm⁻³
After mixing (1 L total): [HA] = 0.10 M, [A⁻] = 0.15 M. [H⁺] = Ka·[HA]/[A⁻] = 1.75 × 10⁻⁵ × 0.10/0.15 = 1.17 × 10⁻⁵ mol dm⁻³ → (b).